1. Field of the Invention
The present invention relates to a semiconductor laser device.
2. Background Art
Conventionally, as disclosed, for example, in Japanese Patent Laid-Open No. 2002-94188 and Japanese Patent Laid-Open No. 11-233882 below, semiconductor laser devices are known which have various improved optical characteristics such as light intensity distribution and light confinement.
Japanese Patent Laid-Open No. 11-233882 discloses a semiconductor laser device including a conductive clad layer, a light guide layer and a low refractive index layer having a lower refractive index than that of the conductive clad layer interposed between the conductive clad layer and the light guide layer. This makes it possible to expand a light intensity distribution in a crystal growth direction and consequently narrow a far-field pattern (FFP) thereof.
Japanese Patent Laid-Open No. 2002-94188 discloses a semiconductor laser device that increases light confinement of light confined in an active layer by making the refractive index of a p-side light guide layer higher than the refractive index of an n-side light guide layer.
However, it is difficult for conventional semiconductor laser devices to increase power conversion efficiency for achieving both a reduction of a threshold current and an improvement of slope efficiency. The present inventor made every effort to research a semiconductor laser device that allows a high-order mode equal to or higher than a first order mode in a crystal growth direction, and came to discover a semiconductor laser device capable of achieving both a reduction of a threshold current and an improvement of slope efficiency.